Refrigerated intake brayton cycle system

ABSTRACT

In an open Brayton cycle, suction air is cooled by refrigeration to a predetermined temperature preferably to at least 50*F. below ambient air temperature. In the case of a conventional refrigeration system with refrigerant evaporation and condensation utilizes ambient air for condensation, the refrigeration is controlled to maintain a fixed temperature differential between the temperature at which the refrigerant evaporates and at which it condenses. If the temperature of the suction air is below the freezing point of water an aqueous solution of a water vapor pressure depressant such as glycol may be used under conditions which avoid, or control, freezing. This aqueous solution may be sprayed on cooling coils in indirect heat transfer or it may be cooled by circulation in indirect heat transfer and then used in direct contact to cool and condense water vapor from the suction air. The condensed water is vaporized, preferably with waste heat and injected into the compressed air stream. The refrigeration system may be a conventional one driven by the shaft or from the power network or it may be one which is driven by a system utilizing waste heat of the Brayton cycle exhaust gases. In a conventional system, multistage refrigeration is preferred. In the use of a solution of glycol the composition is maintained by distillation of water under pressure with utilization of the steam in the air stream between the Brayton cycle compressor and expander to improve output and thermal efficiency. The advantages of suction air refrigeration are especially marked when in combination with regeneration in the Brayton cycle and the advantages of regeneration are greater when in combination with suction air refrigeration. Still greater advantages result from a combination of suction air refrigeraton with both regeneration and gasification of fuels which contain sulfur and particulates. A portion of the refrigeration capacity for suction air cooling may be used for the cooling of electric generators and transformers. Suction refrigeration results in similar advantages when used with a closed Brayton cycle, wherein the working fluid is a dry gas, such as helium, or argon, or the like.

United States Patent [191 Nebgen [54] REFRIGERATED INTAKE BRAYTON CYCLESYSTEM [58] Field of Search 62/93, 208, 209, 210, 211,

[56] References Cited UNITED STATES PATENTS 1,879,685 9/1932 Jaczko60/39.67 2,548,508 4/1951 Wolfner 60/3967 X 2,678,531 5/1954 Miller60/3955 3,621,656 11/1971 Pacault et al. 60/3967 X 3,649,469 3/1972McBeth 60/3955 X- 2,216,690 10/1940 Madden..... 62/208 X 2,734,3462/1956 Dickieson, Jr. 62/217 X 2,888,809 6/1959 Rachfal 62/208 X3,250,084 5/1966 Anderson... 62/208 X' 3,260,064 7/1966 Newton....'62/217 X 2,339,185 l/l944 62/238 X Nettel Primary ExaminerWilliam FIODeaAssistant Examiner-Peter D. Ferguson Attorney, Agent, or Firm-RobertAmes Norton et al.

CONDENSE D WATER 3 Jan. 29, 1974 maintain a fixed temperaturedifferential between the temperature at which the refrigerant evaporatesand at which it condenses. If the temperature of the suction air isbelow the freezing point of water an aqueous solution of a water vaporpressure depressant such as glycol may be used under conditions whichavoid, or control, freezing. This aqueous solution may be sprayed oncooling coils in indirect heat transfer or it may be cooled bycirculation in indirect heat transfer and then used in direct contact tocool and condense water vapor from the suction air. The condensed wateris vaporized, preferably with waste heat and injected into thecompressed air stream.

The refrigeration system may be a conventional one driven by the shaftor from the power network or it may be one which is driven by a systemutilizing waste heat of the Brayton cycle exhaust gases. In aconventional system, multistage refrigeration is preferred.

The advantages of suction air refrigeration are especially marked whenin combination with regeneration in the Brayton cycle and the advantagesof regeneration are greater when in combination with suction airrefrigeration.

Still greater advantages result from a combination of suction airrefrigeraton with both regeneration and gasification of fuels whichcontain sulfur and particulates.

A portion of the refrigeration capacity for suction air cooling may beused for the cooling of electric generators and transformers.

Suction refrigeration. results in similar advantages when used with aclosed Brayton cycle, wherein the working fluid is a dry gas, such ashelium, or argon, or the like.

10 Claims, 3 Drawing Figures BRAYTON CYCLE AIR COMPRESSOR COOLED AIREXPANDER BRAYTON CYCLE R EC UP E RATOR COMBUSTION CHAMBER HOlVBOdVAHCONTROLLER AMBIENT AlR o REFRIGERANT COMPRESSOR 67 AMBIENT AIRPATENTEDJAII 29 I974 BRAYTON CYCLE SHEEI 1 OF 3 BRAYTON CYCLE AIRCOMPRESSOR EXPANDER c 1 GENERATOR Ep TT AT T REc A I R TOO COOLER TRECUPERATOR m II /I s E' FUEL REFRIGERANT L HEATER T INTAKE AIR NH IEXHAUST I 7- C C Is I II 29 28 27 I5 I4 I3 I II 33 23 7 I2 HOT 34 ISTORAGE REFRIG REFRIG TANK COMPRESSOR EXPANDER REFRIG V CONDENSER f 3 4HOT FLASH TANK AMBIENT STORAGE TANK INVENTOR WILLIAM H. NEBGEN ATTORNEYPATENTEDJIIII 29 I974 7 SHEET 2 OF 3 I20 PM; i sTEAM As REOO. FORPROCESS COMPRESSED AIR Ioo PSIG 1 43 PRODUCT 22 5OF 700F I ,sTEAMTURBINE 4| PARTIAL o FUEL OXIDATION i F BOILER GENERATOR REAOTOR 1 WATERL STEAM 39 CONDENSER 50 I RECYCLE BF PUMP BLOWER Fw IsoFi PARTIcuLATEHEATER SCRUBBER H25 REMOVAL EXPANDER COM/PIZESSOR 58 52 F g; 5 GENERATORo NR 800 cOMBusTOR o REFRIGERATED 900 5 A ATMOSPHERIC 54 AIR r rRECUPERATOR REOOPERATOR PURIFIED FUEL GAS EXHAUST 60 J imolt ISOOFtINVENTOR WILLIAM HRNEBGEIN FIG. 2

ATTORN Y -1 REFRIGERATED INTAKEBRAYTON CYCLE SYSTEM 'RELATEDYAPPLICATIONThis is a continuation-in-part of my co-pending application, Ser. No.34,717, filed May 5, 1970, now U.S. Pat. No. 3,668,884 dated June 13,1972.

BACKGROUND OF THE INVENTION In a gas turbine the power output depends onthe suction air temperature and increases as the temperature is lowered,other parameters remaining the same. This suction temperature isnormally that of the ambient air and fluctuates daily, seasonally andwith atmospheric conditions.

When the air entering the suction of a given engine is cooled byrefrigeration the compression ratio and mass flo'w increase and theexpansion ratio and mass flow also increasefso thatthe net shaft outputis increased accordingly. This increase in power output is considerablymore than the power that is needed to effect the refrigeration. For thecombined system of the Brayton cycle and refrigeration cycle the thermalefficiency is not significantly different from that of the Brayton cyclealone. The additional capital expense for refrigeration is often lessthan the value of the increase in power output that results fromrefrigerating the suction air. g

In an open Brayton cycle engine, air enters the engine at atmosphericpressure, is compressed, is heated by being burned with fuel and then isexpanded back to atmospheric pressure. The net work output of the engineis the relatively small difference between two quite large numbers,i.e., it is the difference in the total work' produced by its expanderand the work con- 'sumed by its air compressor. In this discussion, the

open Brayton cycle expander for convenience is referred to as an -airexpander, although the working fluid actually contains the products ofcombustion of the fuel. The work produced by the air expander of a 5.4ratiosimple Brayton cycle engine is about 2.77 times the net work outputof the engine, and when the compressor takes suction at ambienttemperature (for example 100F.) the work consumed by the air compressoris about 1.77 times the network output. If the ambient temperature airis refrigerated before it enters the compressor, the work output of thisBrayton cycle engine increases because the compression ratio increases,and the expansion ratio increases accordingly; the work produced by theair expander therefore increases; and also because the mass flow of airthrough the engine increases, due to the greater density of the coldair. The work which is required to refrigerate the' inlet air must, ofcourse, be deducted from the work which is produced by the Brayton cycleengine, but even when an inefficient single stage refrigeration systemis used, the refrigerated suction engine delivers more usable shaft workthan does the same engine if it takes suction at ambient temperature.

Similar advantages result from refrigerating thev suction of a closedBrayton cycle engine, wherein the working fluid may be dry, and isheated indirectly in an external heat exchanger.

Refrigeration of suction air presents certain problems which arisefromthe condensation of moisture as the temperature of the air isreduced below the dew point.

In the case of a large power facility the quantity of moisture is verylarge. For example, a typical facility to generate 200 megawatts, andreceiving ambient air at F. and 50 percent relative humidity, requiresremoval of 325,000 gallons daily of water when the dew point is reducedto 32F.

Most of this is recoverable as liquid water by cooling the suction airto a temperature which is in the vicinity of the freezing point.Normally this requires refrigeration, for example, by indirect heatexchange with an evaporating refrigerant. Water condenses on the heatexchange surfaces and the runoff is collected and recovered. If the airwere to be cooled by refrigeration substantially below the freezingpoint the vapor would condense to produce ice, or rime, on the coolingsurface. This accumulation in a short time would block the passages forair flow in indirect heat transfer apparatus for air cooling.

In the prior art of cooling air, for example the refrigerated storage offood, icing is prevented or reduced by applying to the heat'exchangesurface a liquid which SUMMARY OF THE INVENTION One aspect of thepresent invention concerns an improved method of heat transfer forcooling and dehumidification of suction air to an open Brayton cycle. Inone embodiment of this method the suction air is caused to pass over aheat transfer surface which is preferably wetted by an aqueous solution,e.g. of ethylene glycol, methanol, etc. The composition of the aqueoussolution which is applied to the surface is controlled to avoidsolidification on the heat transfer surface at the temperature of therefrigerant or cold fluid.

It is, of course, clear that the aqueous solution absorbs the watervapor from the suction air and becomes diluted thereby. In accordancewith this invention the composition and quantity of the solution appliedto the heat transfer surface is controlled, in combination with thequantity of water condensed, so that the composition of the solutionwhen it is diluted with condensate is everywhere on the heat transfersurface a composition corresponding to a freezing point which issufficiently below the temperature of the refrigerant or coolant toprevent ice deposition.

Usually itis advantageous to cool the air in stages to the desiredsuction temperature. The minimum concentration of the aqueous solutionin contact with the Ultimately the final spent solution is regeneratedby I a distillation separation obtaining a more concentrated aqueoussolution to be recycled for application on the heat transfer surface.When, as for example in the case of a glycol, the aqueous solute is lessvolatile than water the latter is removed in the overhead vapor of thedistillation whereas, for example in the case of methanol,

the solute, being the more volatile component, is recovered in theoverhead fraction, leaving the water in the bottoms. From this overheadvapor the methanol is condensed and recycled.

The choice of an aqueous solute in accordance with this inventiondepends on the temperature range of the air cooling stage. Ethyleneglycol is a preferred solute, at temperatures above about 40F. Belowthis temperature the viscosity of the aqueous solutions of glycol ishigh. At lower temperatures methanol provides the desired freezing pointdepression without excessive viscosity or too high vapor pressurewhereas at higher temperatures methanol is too volatile.

In a second embodiment of this invention there is direct transfer ofheat from the air to the aqueous solution at each stage of cooling,together with indirect heat transfer from the aqueous solution to arefrigerant or coolant. The aqueous solution is recycled between thesetwo heat exchange operations and it serves thereby as a medium for heatexchange as well as for absorption of condensed water vapor from theair. The concentration of the aqueous solution in each cooling stage iscontrolled by the withdrawal of dilute solution and the return of a moreconcentrated solution to replace the dilute solution whichis withdrawn.The difference in the water content of the dilute solution and theconcentrated solution represents the water vapor that has been condensedfrom the air.

In this embodiment, as in the first embodiment, the composition of theaqueous solution is controlled so that at the temperature of therefrigerant or coolant, freezing does not occur on the heat transfersurface which in this embodiment separates the refrigerant, or coolant,and the aqueous solution.

Contact between the aqueous solution and the suction air is by means ofa packed bed or other apparatus and the scope of the invention is notlimited to any particular form of apparatus. The transfer from theaqueous solution to the refrigerant or coolant is preferably in a shelland tube heat exchanger but again the invention is not limited thereto.

At any stage of air cooling which is above the normal freezing point ofwater'there is no need for an aqueous solution to control the freezingon the heat transfer surface in either embodiment of this invention andwater could be recirculated in the second embodiment. However, theaqueous solution of either embodiment dehumidifies as well as cools theair. For this reason it is advantageous to utilize an aqueous solutioneven in the higher temperature stages of cooling above 32F. since thistends-to remove, at a given temperature, a larger amount of water vaporfrom the air, and thus reduces the work of refrigeration. Anotheradvantage of using an aqueous solution of a freezing point depressanteven where cooling would not result in ice deposition is that it is notnecessary to change the composition of the recirculated coolant astemperatures change and this simplifies equipment and operation.

While a freezing point depressant is preferred, the present invention inits broader aspects is not absolutely limited to such a material for theprevention of formation of solid ice on heat exchange surfaces. It ispossible to use a material which is relatively immiscible with water,for example, a liquid hydrocarbon. In this case the freezing point ofcondensed water is not actually depressed but the flow of thesubstantially nonsolvent liquid keeps ice crystals very small and ineffect keeps them in a dispersed form so that they do not deposit assolids on the refrigerating equipment. Separation of water from anon-solvent can be effected simply and economically by raising thetemperature above the freezing point of water, forming liquid water,which can be separated by decantation or other conventional methods ofseparating water from non-solvent liquids. It will be noted thatregardless of how ice formation is controlled, relatively pure water isproduced.

Another aspect of this invention pertains to the utilization ofcondensate water in an open Brayton cycle for improvement of thermalefficiency and of power output capacity. One method to use thiscondensed water is to spray it into the air compressor of the Braytoncycle and another method of utilization is to inject the steam resultingfrom the vaporization of the condensate into the stream of air from theBrayton cycle compressor. It should be noted that increase of thermalefficiency and power output capacity do not necessarily involve the sameeconomic considerations. Thermal efficiency increases are largelyfactors which lower fuel cost. However, for certain uses, such asBrayton cycle installations for power peaking in electric generatingplants, increases in power output may be more valuable than savings infuel cost. As has been pointed out above, and will appear below, not allof the features of the present invention increase both thermalefficiency and power output capacity. In the case of the use ofcondensate water, there is the fortunate situation that both factors areimproved. It should be noted that the present invention in the aspectjust set out need not be limited to using all of the condensed water inthe Brayton cycle and that the invention, therefore, does includecombinations of features in which only part of the condensate water isused in the Brayton cycle. However, as the amount of condensate water isnormally less than that which can be effectively used in the openBrayton cycle, it is usually preferable to use all of the condensatewater.

If the water is utilized as steam to increase the volume of gas to theexpander, the. steam must be generated at a pressure equal to, orslightly higher than, the Brayton cycle compressor discharge and itshould be admitted at, or prior to, the combustor. The heat that isneeded to generate the steam preferably is obtained by waste heatrecovery from the stack gases. Condensate which is obtained as liquidwater, either from condensation above the temperature of ice formation,or by recovery from an aqueous solution of a solute which has volatilitydiffering from that of water, is evaporated under a pressure which is atleast as high as that of the Brayton cycle compressor discharge. Whenthe condensate water is in the form of a solution of glycol orothersolute which is less volatile than water the water is distilled atthe pressure required for injection and the vapor is rectified to theextent necessary to minimize the loss of solute. The rectified watervapor represents the steam which is then suitable for injection, thedistillation and rectification heat preferably being obtained from theBrayton cycle exhaust, though other sources of waste heat may be used.

This invention is not limited to any particular refrigeration system,but a multistage refrigeration system in many cases is preferable sinceit is more efficient than a single stage system because all of the heatwithdrawal is not at the lowest temperature.

Still another aspect of this invention relates to the improvement whichresults from the combination of refrigeration of suction air at least50F. below ambient with recuperation of the waste heat from the turbineexhaust in a regenerator. Recuperation or regeneration to improve theenergy efficiency of a simple Brayton cycle by utilizing some of thewaste heat to reduce the amount of fuel required to raise the gases tothe turbine inlet temperature is not unknown, and it is an advantage ofthe present invention that recuperation can be used, and used even moreeffectively, than in the prior art.

The quantity of heat recuperated is limited by the temperaturedifference between the turbine exhaust and the compressed air whichabsorbs the heat. When as in accordance with this invention, the suctiontemperature is reduced by refrigeration of the air, the temperature ofthe compressed air is lowered. This increases the capacity of thecompressed air to absorb waste heat from the exhaust gases. There is anenergy saving of one Btu for every Btu of transfer in the regenerator.Consequently the combination of heat regeneration and refrigeration toreduce the compressor suction temperature is an important advantage ofthis invention.

Still another aspect of this invention relates to keeping asubstantially constant differential between the temperature of thesuction air and that of the ambient air, regardless of the ambient airtemperature. This permits optimum utilization of the refrigerationsystem to improve the power output of theBrayton cycle and to maintainthe optimum improvement regardless of weather conditions.

In accordance with this last aspect of the invention, I employ theambient air as the heat sink of the refrigeration system, i.e., as thecoolant of the refrigerant condenser. The vapor pressure in thecondenser varies with the temperature of the coolant air, and thisrepresents a corresponding variation of the discharge pressure of therefrigeration compressors. Since it is desirable that the suction airtemperature be a fixed amount below the ambient air temperature, thepressure in the evaporator also varies, the pressure being higher with ahigher ambient air temperature. The refrigerant com-- pressor is aconstant volume device, but the density of the refrigerant vapor variesinversely with its pressure so that, without suitable control, the massflow of refrigerant is similarly variable. As a consequence, the

compressor of a system which is designed to cool the suction air by,say, 50F., at an ambient temperature of 95F, will not have the capacitytocool the air by the same amount when the ambient temperature is 40F.Accordingly, in the system of this invention, I provide a means forthrottling the vapor from the evaporator so that at the highertemperatures the flow of vapor is reduced, while at lower ambienttemperatures it is in-.

creased to compensate for the inverse tendency which is a consequence ofthe changes of vapor density.

One method of throttle control is by adjustable guide vanes in the inletto the compressor. The angle of the vanes and the space between them isadjusted manually or automatically to control the flow of therefrigerant vapor and, thereby, the rate of evaporation, so that thereis maintained a substantially constant difference betweenthe temperatureof the Brayton cycle suction air and that of the ambient air. The signaloutput of two temperature sensors, one in the ambient air and the otherin the compressor suction, canbe used to operate a servo system whichpositions the inlet guide vanes.

In a multistage system of refrigeration in which the mass flow'ofrefrigerant in each compression stage is dependent on the other stages,the preferred embodiment is one which provides throttle control at eachstage. For example, when the range of ambient variation is 50F at themaximum ambient temperature the compressor should be throttled to aboutone-third of its capacity and should be wide open at the lowest ambienttemperature.

When it is desired to refrigerate the suction air to temperatures as lowas -40F. or less it becomes difficult to find non-volatile substanceswhich, in aqueous solution, are sufficiently fluid at .these lowtemperatures. Accordingly, it is an object of this invention to removemoisture from the air by means of an aqueous solution at the next highertemperature stage of refrigeration so that the air which enters thelowest temperature stage of refrigeration has a dew point which is solow that the final stage may be by means of a heat transfer surfacewhich remains dry, i.e., free of ice condensation without theapplication of an aqueous solution. I

This is achieved, in accordance with this invention, by control of theconcentration and temperature of the aqueous solution in contact withthe air in the next to final stage of refrigeration, in combination withthe final stage temperature. The. advantage gained from this method ofstaging of the air cooling is that the aqueous solution does not have tobe used at the lowest temperature of the air, at which the solutionviscosity may be excessively high. For example, a 60 percent glycolsolution is used at -32F. to cool, and remove moisture from, airwhichmay then be further cooled dry to 45F. At 32F. the viscosity of theaqueous solution of glycol is centipoises, which is not too heavy forprocess use, whereas at'the lower temperature of -,45F. the viscosity is500 centipoises, which is excessive. The control of these temperaturesin combination with the aqueous solution composition thus enables thecooling of the air to a temperature which is not otherwise practical.

Still another aspect of this invention relates to the utilization ofdirty fuels as the source of energy isan open Brayton cycle. Ina-prefer'red embodiment suction air to the compressor is refrigerated toat least 50F. below ambient. The compressed air is divided, into twostreams, one stream for the partial combustion and gasification of thedirty fuel, and the other for the combustion in the Brayton cycle engineof the gasified fuel after it has been cleaned.

Gasification and combustion occur at a temperature above 2,200F. and arecarried out in apparatus which is Well known and which may be suitablefor either coal or oil. One known method and apparatus is described inthe Khristianovich et al. US Pat. No. 3,287,902, Nov. 29, 1966, to whichreference is hereby made. The patent, while making general reference tothe use of a gas turbine, is primarily directed to the combination ofthe cleaning of the dirty fuel with a steam turbine. There is, ofcourse, no suggestion of the other features of the present invention,namely the combination with refrigerated suction, compressors, etc.Prior to combustion the compressed air is heated by regenerationutilizing the waste heat of the Brayton cycle turbine exhaust. When airis used in the gasification of fuel, the ratio of air to fuel must behigh enough to maintain the reaction temperature. Subject to thislimitation, the ratio should be minimized to retain the maximum heat ofcombustion in the products. The heat which is absorbed by the combustionair in regeneration contributes to a reduction of the air requirementand a corresponding increase of heat retention.

The products of partial combustion are cooled in a pressurized wasteheat boiler and boiler feed water heater and are scrubbed and cleaned toremove particulates and sulfur compounds or, in the case of some oils,nickel and vanadium compounds. The cleaned gases then are heated in asection of the regenerator, flowing in parallel with the air from thecompressor. The heated cleaned gases are burned with preheated air inthe combustors, and the hot products of combustion then undergoexpansion in the turbine in the case of an open Brayton cycle or theheat exchanger heating a working fluid in the case of a closed Braytoncycle.

The system of this invention provides unique advantages in efficiency.By refrigeration of the suction air to the compressor, the compressedair to the regenerator is cooler and has a much greater capacity forabsorption of waste heat than does the equivalently compressed ambienttemperature air. The cooled products of fuel gasification offeradditional capacity for heat absorption, and as a consequence, theexhaust gases from the regenerator are considerably cooler than in asystem that does not regeneratively heat the gasification products. I

The purified fuel gases, when used in a Brayton cycle, suffer nodisadvantage by having their caloric content so greatly reduced becauseof dilution by the nitrogen of the partial oxidation air. These fuelgases, when preheated by the waste heat available from the regeneratorof the Brayton cycle, have a flame temperature which is considerablyhigher than that which the Brayton cycle turbine can endure, and excessairis still needed for quenching, although not to the same extent aswhen higher heat content fuels are used. All of the allowabletemperature of the purified low heat content fuel gas is, therefore,effectively used in the Brayton cycle, whereas its relatively low flametemperature makes it uneconomical to use for many other purposes, suchas for steam generation. In other words, the refrigerated suction andregenerated air and fuel gas features of the present invention resultsin being able to use effectively in a Brayton cycle fuel gas of low heatcontent. In the present application the broad combination of productionof clean, lower heat content fuel gas from dirty fuel with a Braytoncycle generally is not covered since this broad application is describedin my co-pending application Ser. No. 44,673. It is, however, anadvantage that the other features of the present invention can be usedwith the partial oxidation of dirty fuel, which in a number of casespermits further economies in fuel cost.

faced with a number of problems: One is that of peak power, which may berequired for only a few hours a day and/or a few days a year. Braytoncycle systems can start up quickly and are ideal for peaking powerpurposes. Another factor is the increasing stringency of regulation forenvironmental pollution. Stack gas cleanup processes are currently beingdeveloped, but they all are expensive, so at present the mostsatisfactory method of pollution control is to use clean fuels. An openBrayton cycle requires quite clean fuel in any event because somepollutants are intensely corrosive to most metals and other materials ina gas turbine or heat exchangers for the working fluid of a closedBrayton cycle at the temperatures at which the turbine or heat exchangeroperates, whereas the same pollutants frequently do not present suchsevere corrosion problems at the much lower temperatures of the surfacesof steam boilers. Therefore, Brayton cycles, particularly open Braytoncycles, have to use relatively clean fuel regardless of environmentalpollution requirements. This has presented an interesting economicfactor in the use of Brayton cycle engines in power plants. Forenvironmental reasons the fuels used in any generating plant must beclean, and since Brayton cycle plants, such as open Brayton cycleplants, are usually much cheaper than steam plants, it is commonpractice in many large central plants to use Brayton cycle plants, whichwere originally intended for peak power production, for a much longerportion of the year. The increases in Brayton cycle thermal efficienciesand power outputs made possible by the present invention thereforeassume great economic importance in this large and growing field.

Both thermal efficiency and maximum power output are important. Therewill be described below a preferred embodiment in which the degree ofcooling and the compression ratios are optimized for maximum efficiency.In a more specific aspect of the present invention such optimizedsystems or close approaches thereto, which will be described below,'areincluded. However, in broader aspects the present invention includes theessentials of cooling by means of multistage refrigeration systems. Itis an advantage of the present invention that it can'be used in variousdegrees of sophistication and optimization depending on the besteconomic compromise for a particular use or a particular installation.

Maximum refrigeration efficiency is obtainable by a refrigerating systemwhich forms the subject matter of the elected invention of the parentapplication, Ser. No. 34,717, above referred to. This system is therereferred to as the Treadwell System, and this nomenclature will be usedin the same sense in the present application. This most highly effectiverefrigeration system in combination with the other features of the pres-I ent invention is included in a more specific aspect of the presentinvention, though the refrigeration system as such is, of course, notclaimed herein. The combination of the principal features of the presentinvention with the Treadwell system of refrigeration is in no sense anaggregative use of two isolated features or subcombinations of features.

When the present invention is used for electric power generation, thelargest single field at present, as has been set out above, a furtherrefinement is possible and is of practical importance in some cases.Because of the large quantities of incoming air, a relatively largerefrigeration system is needed. A unit of refrigeration capacity in suchlarge systems is much more economical carbon. These fluids can be cooledby a portion of the capacity of the large refrigeration system which isused for cooling the incoming air in the Brayton cycle. This utilizationof a very small part of the large refrigerating capacity permits theeconomical sub-ambient cooling and the consequent increase in capacityof generators,

transformers, etc. It is also necessary to cool lubricating oil inBrayton cycle turbines, and the same considerations apply'as this can bedone more economically by the relatively very large refrigeration systemnecessary in the present invention.

In thedescription of the preferred embodiment the description of theparticular Treadwell system of refrigeration will be repeated as in theparent case, but, as has been pointed out above, this is only onetypical refrigeration system albeit one capable of giving optimumresults, and the invention is not limited in its broader scope to theparticular Treadwell system but includes any refrigerating system havingthe limitations of cooling and prevention of ice or other solidsformation which has been discussed in detail above. I

Most of the preceding discussion has been directed Particularly to arefrigerated suction regenerated open Brayton cycle engine. Very similarimprovements in output and efficiency result when refrigeration andregeneration are applied to a closed Brayton cycle engine, in which thecooling fluid, which may be a dry gas such as helium, argon, etc., isheated indirectly in an external heat exchanger. Such a closed Braytoncycle is sometimes used with atomic power generators.

Because of the greater flexibility in plant arrangement, significanteconomic advantage is obtained when an auxiliary fluid, such asDowtherm, is used to transfer regeneratedheat from the expander exhaustto the compressor discharge.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows in purely diagrammaticform the combination of cooling the suction of an air compressor for aregenerated open Brayton cycle, and shows as the refrigerating systemthe Treadwell system; I

FIG. 2 shows in purely diagrammatic form a system for the use of dirtyfuel ina Brayton cycle, and

FIG. 3 is a diagrammatic showing of a conventional refrigeration systemrefrigerating the intake to the air compressor of a Brayton CycleSystem.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 3 illustratesdiagrammatically a simple, conventional refrigerating system-withrefrigerant evaporation and condensation, the latter being by heatexchange with ambient air. Ambient air passes through the refrigerantevaporator 61 where it is cooled to a predetermined temperature, such asat least 50F. below the temperature of the ambient air, in the presenceof a freezing point or vapor pressure depressant in the form of anaqueous solution when a predetermined temperature is sufficiently low topresent the possibility of water from the ambient air condensing out andfreezing. Water condensed out is'passed through a conduit to a point inthe Brayton cycle system between air compression and turbo expansion.This will be described in more detail below. The air passing through theevaporator 61, and cooled therein, is shown leaving through a conduit atthe top of the evaporator. As indicated, this cool air goes to the inletof a Brayton cycle air compressor, which is shown diagrammatically asthe compressor is a conventional piece of apparatus and the exactmechanical construction of a particular compres-' sor forms no part ofthe-present invention, which includes the use of any well known Braytoncycle air' compressor or compressor system.

The refrigerant vapors leave through conduit 62, passing through athrottling valve 75 and thence through the conduit 63 to a refrigerantcompressor 64 driven by a motor 65. The compressed refrigerant vaporspass through conduit 66 into the top of the condenser 67 where they arecooled by heat exchange by ambient air as indicated. This results incondensation of the refrigerant vapors to liquid refrigerant whichpasses through pipe 68 and expansion valve 76 into the refrigerantevaporator 61.

There are two temperature sensors, one 69 for the ambient air enteringthe evaporator 61 and the temperature therein, which is sensed byanother sensor 70. These sensors connect to inputs 71 and 72, which maybe wires, to a controller 73 which converts them to a differentialsignal 74 which operates a servo mechanism 76 driving the throttlingvalve 75. The controller 73, of conventional design, is set for thepredetermined temperature between sensors 69 and which sense thetemperature of refrigerant condensation and evaporation respectively.The temperature of the ambient air is, of course, substantially that ofthe condensed refrigerant in a condenser 67. As is common indifferential controllers, controller 73 will put out a signal 74 onlywhen the differential between the temperature sensed by sensor 69 andsensor 70 depart from the predetermined value for which the controller73 is set. As is customary in such control circuits, the signal 74 is ina different phase depending on whether the temperature differentialbetween sensors 69 and 70 is greater or less than the predeterminedvalue set in the controller. This signal operates the servo mechanism 76to vary the setting of the valve 75 and hence the throttling of therefrigerant vapor. As soon as the throttling has brought the temperaturedifferential between sensor 69 and 70 to the predetermined value, thesignal 74 ceases and the throttling therefore maintains thepredetermined temperature differential regardless of the temperature ofthe incoming ambient air.

In the Summary of the Invention a throttling method with adjustableguide vanes is described. This, of course, performs precisely the samefunction as a simple throttling valve 75. The latter, however, issimpler to illustrate in a purely diagrammatic drawing such as FIG. 3.The invention is, of course not limited to any particular special designof throttling mechanism. Both valves and vanes are well known throttlingdevices.

The diagrammatic illustration of the Brayton cycle system is similar tothat shown in FIG. 1, but the cooling of the air is effected, asdescribed above, in a refrigerant system involving an evaporator andcondenser.

From the Brayton cycle air compressor the compressed air enters arecuperator together with condensate water from the refrigerantevaporator. In this recuperator, which, as shown, receives hot exhaustgases from the Brayton cycle expander, the temperature is above theboiling point of the condensate water and thus transforms it into watervapor, which, mixed with the heated compressed air, then passes throughthe combustion chamber and thence to the inlet of the Brayton cycleexpander, in which it expands and the hot exhaust gases flow through therecuperator, as has been described. The Brayton cycle air compressor isshown as driven from the Brayton cycle expander from which a shaftextends, shown as broken, to any desired device for utilizing the power.In FIG. 1 this shaft is shown as going to a generator but in FIG. 3, inorder to conserve drawing space, the generator is not shown.

FIG. 1 will next be described and will be followed by the computationfor operation at maximum efficiency. These computations are more clearlyunderstandable after a description of the actual machine elements.

On this figure air at ambient temperature T enters the air cooler at thepoint marked Air Intake, and is cooled to a temperature T which is atleast 50F. below the ambient temperature at which it is intended tooperate the engine. The cooled air enters the air compressor, in whichit is compressed through the compression ratio r The ratio r iscalculated for optimum operating conditions below in the section settingforth computations after description of the drawing. The compressed airenters the regenerator at a discharge temperature whichis determined byr and suction temperature T In the regenerator the air is heated by heatexchange with the exhaust from the Brayton cycle expander and passesinto a conventional Brayton cycle combustion chamber. In this chamberfuel is burned and the temperature of the compressed air is raisedfurther to T which is the maximum temperature that the-materials of theexpander can withstand. The maximum permissible level of T is in nosense changed by the present invention.

The compressor is driven by the expander. The difference in the workwhich is produced by the expander and the work which is required by thecompressor constitutes the net work output of the Brayton cycle. This issymbolized on the drawing by the power output shaft being connected toand driving an electric generator.

The expander exhaust gases go to a regenerator, which they leave at atemperature T T is determined by the discharge temperature of thecompressed air and by the temperature differential AT indicated. Theexhaust gases then pass through a refrigerant heater in which pump 2keeps the refrigerant liquid at a sufficient pressure so that it doesnot boil. The amount of liquid which goes to the heater is determined bythe adjustment of valves 5 and 6. In the heater the liquid refrigerantis heated up to temperature T minus the small temperature differentialAT which is required for heat exchange. The exhaust gases then areexhausted as indicated, ordinarily at ambient temperature plus the samesmall temperature differential AT The hot refrigerant liquid flows fromthe refrigerant heater into a suitably insulated hot storage tank 1.

From time to time valve 4 is opened, and a batch of hot liquid istransferred from hot storage .tank 1 to hot flash tank 3. The liquidholding capacity of hot storage tank 1 is sufficiently greater than thatof hot flash tank 3 to permit substantially continuous operation. Thedrawing is diagrammatic, so only a single hot flash tank is shown, butmultiple tanks can be used, if desired.

In not flash tank 3 the heated refrigerant liquid, initially under suchpressure as may be needed to prevent boiling in the refrigerant heater,flashes at decreasing temperatures and pressures until it reaches aminimum temperature and pressure, normally about ambient temperature.Valve 10 then is opened, and the remaining unvaporized liquid ispermitted to flow into ambient storage tank 11.

Three refrigerant expanders 7, 8 and 9 constitute the power generatingportion of the refrigeration system. The pattern of flow through theexpanders is controlled by valves 12, 13, 14, 15, 16, 17, 18 and 19. Atfirst, when the vapor in the hot flash tank is at maximum temperatureand pressure, valves l2, l4, l7 and 19 are opened, and valves 13, 15, 16and 18 are closed. As a result, refrigerant vapor passes in seriesthrough expanders 7, 8 and 9. These expanders drive correspondingrefrigeration compressors 21, 22 and 23. This is symbolized on thedrawing as a common shaft connecting expander 7 and compressor 23, acommon shaft connecting expander 8 and compressor 22, and a common shaftconnecting expander 9 and compressor 21.

At the start, the temperature and pressure in hot flash tank 3 is at amaximum and the flash vapor passes through expanders7, 8 and 9 inseries. At the same time, the pressure and temperature in cold flashtank 30 is at a maximum, and the load on refrigeration compressors 21,22 and 23 is at a minimum. The pattern of flow through these compressorsis controlled by valves 20, 24, 25, 26, 27, 28, 29 and 33. At the startthe three compressors operate in .parallel, valves 20, 24, 26, 27, 29and 33 being open, and valves 25 and 28 being closed. The load oncompressors 21, 22 and 23 increases as the temperature and pressure ofthe refrigerant in cold flash tank 30 drops. When expanders 7, 8 and 9can no longer produce sufficient power to drive the compressors, valves17, 19, 20 and 26 are closed. This has the effect of cutting offexpander 9 and compressor 21; and now expanders 7 and 8 in series drivecompressors 22 and 23 in parallel.

After a further lapse of time, the pressure and temperature of therefrigerant in hot flash tank 3 and of the refrigerant in cold flashtank 30 drops. When the load on compressors 22 and 23 increases and thepower output of expanders 7 and 9 decreases to the point where theexpanders can no longer drive the compressors,

valves 13 and 15 are opened and valve 14 is closed.

Now expanders 7 and 8 in parallel drive compressors 22 and 23 inparallel.

After a further drop in the temperature and pressure of the refrigerantin tanks 3 and 30, valves 27 and 29 are closed and valve 28 is opened.This results in two expanders, 7 and 8, in parallel driving twocompressors, 22 and 23, in series.

When the temperatures and pressures in tanks 3 and 30 have dropped stillfurther, valves 16, 19, 20 and 25 are opened and valve 24 is closed. Nowthe three expanders 7, 8 and 9 operate in parallel to drive the threecompressors 21, 22 and 23 in series. It will be noted that during thewhole operation exhaust vapors from the expanders and compressed vaporsfrom the compressors flow into a conventional water cooled refrigerationcondenser 34, where the vapors are condensed at practically ambienttemperature. The condensate is discharged into ambient storage tank 11.When expanders 7, 8 and 9 no longer have sufficient power to drivecompressors 21, 22 and 23, valve .10 is opened, and the unvaporizedliquid in hot flash tank 3, now at substantially ambient temperature,also is discharged into ambient storage tank 11. The unvaporized coldliquid in cold flash tank 30 is discharged into cold storage tank 31through valve 35. As in the case of hot storage tank 1, cold storagetank 31 should have sufficient capacity so that continuous operation ispossible.

In the meantime pump 32 continuously has been pumping cold refrigerantliquid from cold storage tank 31 through the air cooler, which has beenmentioned above. Flow of the cold liquid is controlled by valve 36. Itwill be seen from the drawing that the refrigerant liquid leaves the aircooler at substantially ambient temperature and flows into ambientstorage tank 11, in which it is joined by the condensate which is formedin refrigeration condenser 34. Valves l and 35 now are closed and valves4 and 6 are opened. A new batch of refrigerant liquid from hot storagetank 1 thus'is introduced into hot flash tank 3 and a new batch ofambient temperature liquid thus is introduced into cold flash tank 30.Therefrigeration cycle then is repeated. The system is self-regulating.If temperature T at the inlet of the air compressor tends to increase,the temperature of the compressed air entering the recuperator alsoincreases and so, likewise, does T This, in turn, heats the refrigerantliquid to a higher temperature. The flashing of this hotter liquid inhot flash tank 3 produces more power which in turn reduces thetemperature of the refrigerant in cold storage tank 31 and lowers T IfT; tends to decrease, the process is reversed. This self-regulation isan advantage when the Treadwell System of refrigeration is combined withthe recuperated Brayton cycle.

The preferred embodiment shown by the drawing utilizes all of theadvantages of a full Treadwell System and represents a preferredmodification, but the invention is not limited to using all of theadvantages, and may use only part of them.

The following computations are made in conjunction with the combinationof the cooled inlet Brayton cycle has been stated, as a refrigerationsystem forms the claimed subject matter of the parent application abovereferred to. The computations set forth quantities and values of certainof the quantities on the drawing, such as, for example, r Thecomputations, however, in part are applicable to other refrigerationsystems and are not all necessarily limited to the combination with theTreadwell system refrigeration.

The heat value of the refrigeration work (W which is required to cool aprocess stream (for example, a lb. .mol of gas, typically air) fromambient temperature (T,,) to some chosen lower temperature (T is 2 In A-M C (TS-ATE) where C the molal specific heat of the gas (for air about7.0); T the chosen condensing temperature;

AT the chosen temperature difference between the with the Treadwellsystem of refrigeration, which, as l 5 318 BTU/lb. mol.

For any chosen refrigeration system a coefficient of performance C (at aparticular T can be calculated, where C is the ratio of W (in heatunits) to the heat removed from a lb. mol of gas when the gas is cooledfrom ambient temperature T, to a chosen lower temperature TMathematically C [W,;]/[ Cp( T T and for the assumed set of conditions,

C R [3811/ [71)(5 60 40 0) 034 BTU of work required for each BTU whichis removed in cooling the gas. Although for the chosen system C isdependent to some extent on the values of Cp, T AT T and E it isstrongly dependent on T As an illustration, when the values of Cp, T ATT and E; are the same as in the previous example, but T is 450R ratherthan 400R, C 0.254 rather than 0.34. v

In the heat recovery system of the present invention, the heat value ofthe recovery work (W which is produced from the heat released by aprocess stream (for example a pound-mol of gas, typically air) as thestream cools from a super-ambient temperature (T to ambient temperature(T is (T -AT W =C E (ll'l C where E -is the chosen efficiency of therefrigerant expander, and AT is the chosen temperature differencebetween the gas and the refrigerant.

As an example, assume that E 0.8, AT 50, T

580R, and that it is necessary that the system produce 381 BTU of workper lb. mol,

W 7.0 X 0.8 [(T,; 580 (In 1)] 381 BTU/lb.mo1,

from which T 950R.

For any chosen heat recovery system a coefficient of where C is theratio of W (in heat units) to the heat which becomes available when alb. mol of gas cools from an initial temperature T to ambienttemperature T,,. Mathematically, C [W ]/[C T -T and for the assumed setof conditions,

which is produced from each BTU of available heat.

For the chosen system, C is somewhat dependent on the values of Cp, E ATT, and T but it is strongly dependent on T As an illustration, when thevalues of Cp, E AT T,, and T are the same as in the previous example,but T is 900 rather than 950R, C 0.114 rather than 0.14.

The ambient temperature power producing refrigerant liquid is usedcountercurrently to cool the gas which is discharged from a gascompressor, and the ambient temperature power producing refrigerantliquid is heated thereby. When the gas suction temperature and the gascompression ratio are suitably matched, the

1 heat of compression of the gas heats the refrigerant power liquid to atemperature which is high enough so that the power liquid provides allof the work which is needed to refrigerate the gas which is about toenter the gas compressor, and no external work is needed toopperformance C (at a particular T can be calculated,

15 erate the refrigeration cycle. As an alternate the refrigerationcycle portion of the system may be powered in whole or in part by anindependent motor or steam turbine driver. When the heat of gascompression provides the work of refrigeration, T is equal to the gascompressor discharge temperature, and T (T /E (r l) T wherein E is theefficiency of the gas compressor; r is the gas compression ratio; and nis the numerical value of adiabatic exponent (k-l )/k (for air, k 1.4,and n 0.286). When for a desired compression ratio r it is desired todetermine the matching T a trial T is'selected and a corresponding T iscalculated from the preceding formula. The refrigeration work W which isrequired for a chosen refrigeration system to cool the air to the trialT is calculated by the method previously explained. This W is comparedto the calculated heat recovery'work W which is produced by a chosenheat recovery system (using the calculated T which corresponds to thetrial T A series of values of T is tried until the refrigeration workwhich is required for the trial T is equal to the heat recovery workwhich is produced when the corresponding calculated T is used.

As an example, assume that a compression ratio of 15.0 is desired andthat the self-driven Treadwell System is to be used. Several values of Tare tried, which finally converge on 400R, and as a check, this valuefor T together with the desired value of 15.0 for r is substituted inthe previously given equation u (TS/EC) '0" sln substituting,

T (400/185) (15.0 l) 400, from which T 950R. It was previously shownthat with the Treadwell System, when T 950R, the work which is producedby the heat recovery system supplies the work which is required by therefrigeration system when T 400R.

With this suction temperature the gas compression requires only 7 l .5percent of the single stage adiabatic work which is required whensuction is taken at 560R. in the prior art a compression ratio of l5.0cannot be achieved in a single stage compressor with ambient temperature(560R) suction because the discharge temperature of l,330R (870F) ismuch too high, and because far too much compression work is consumed, soa compression ratio of this magnitude usually requires two expensive,intercooled stages of compression. However, when the Treadwell System isused to cool the suction gas to 400R, the same compression ratio of .0is readily conducted in a single stage compressor which produces adischarge temperature of only 950R (490F), and at the same time the network is less than the work which is required by the more expensive twostage compressor. If other less efficient refrigeration and heatrecovery systems are used in place of the Treadwell System, morerefrigeration work is needed to cool the suction to 400R, and less heatrecovery work is produced from the T of 950R. Therefore, the heatrecovered cannot provide refrigeration to a temperature as low as 400R,and the net gas compression work is greater.

When the Treadwell System is used to cool the gas which is about toenter a gas compressor, the subsequent work of adiabatic compressionclosely approximates the work of isothermal compression when theisothermal compression process is conducted at ambient temperature. Infact, if AT and AT are made infinitely small, and T is made the same asT when the Treadwell System is used to cool the suction gas the work ofadiabatic compression exactly equals that of ambient temperatureisothermal compression.

lsotherrnal compression requires the least amount of work because intheory the process is reversible thermodynamically. With adiabaticcompression, the gas which is discharged from the compressor is at ahigher temperature than the gas which enters the compressor, and theheat energy which is required to produce this increase in temperatureis' provided at the expense of additional work energy which has beendelivered to the compressor. The compressed gas is discharged from thecompressor at a relatively low temperature level and its heat normallyis wasted by being rejected to cooling water in an inter or an aftercooler. The direct rejection of this heat to cooling water is acompletely irreversible process thermodynamically. By contrast, in theheat recovery portion of the Treadwell System heat is also rejected tocooling water, but only after it has produced work in the refrigerantexpander. As a result, in the Treadwell System, in theory the heatrejection is completely reversible thermodynamically. Similarly, in therefrigeration portion of the Treadwell System, in theory the heatrejection is completely reversible. When in theory the Treadwell Systemis used with an adiabatic gas compressor, the gas initially is atambient temperature and after compression and heat recovery is also atambient temperature; the refrigeration process is reversible; the heatrecovery process is reversible; and the adiabatic compression process isreversible. Since the final temperature of the compressed gas is thesame as its initial temperature, and since in theory all of theprocesses involved are reversible, in theory adiabatic compression usingthe Treadwell System is equivalent to isothermal compression.

It will be noted that when the compressed gas supplies the heat whichfurnishes the work which is required by the refrigeration system, thesystem is selfregulating. If the gas compressor discharge temperaturerises, more heat is available, more work is developed and morerefrigeration work is available to lower the temperature of the gaswhich is about to enter the compressor. Whenthis temperature is lowered,the temperature of the gas which is discharged from the compressor is inturn lowered. If the gas compressor discharge temperature falls, lessheat is available, less work is developed and less refrigeration work isavailable, so there is an increase in the temperature of the gas whichis about to enter the compressor, and this in crease in turn raises thetemperature of the gas which is discharged from the compressor. Thisautomatic selfregulation is an important operating advantage of thisaspect of the present invention.

The refrigeration system also can be used to cool substances other thangas. In such a case heat from another source may be used to raise thetemperature of the refrigerant power liquid to a level high enough sothat it will provide all the work which is needed by the refrigerantcompressors. However, work is saved to the ex tent that waste heat isfurnishing at least some of the work for the refrigeration system, eventhough it may not be all of the work.

When the Treadwell System is used to cool the gas entering a gascompressor, the heat of gas compression need not be the only source ofheat for the power pro- 17 ducing refrigerant liquid. There may be othersources, which further can increase the amount of self-drivenrefrigeration that can be produced, and this can permit a still lowergas compressor inlet temperature, with a still further saving incompressor work.

The combination of the Treadwell System with a Brayton cycle engineconstitutes the optimum form of the present invention wherein the airwhich is about to enter the compressor of a recuperated Brayton cycleengine is refrigerated and all the work of refrigeration is provided bythe heat which is recovered fromthe exhaust air which is'leaving therecuperator or regenerator of the same engine. According to thepresentinvention, it has been discovered that the maximum Brayton cyclework is produced when r has an optimum value defined by optimum where E(r "/r,, (the expansion ratio r,. is smaller than the compression ratior because of parasitic pressure losses in the system); E and n are aspreviously defined; E is the air expander efficiency; T is the airexpander inlet temperature; and T is a' chosen suction temperature,which is usually selected for practical reasons, such as the cost andthe performance of available refrigeration equipment.

It has been discovered according to the preferred embodiment of thepresent invention that if the improvement in performance is to be ofpractical significance,

18 haust air which is leaving the recuperator and is, therefore, 120F.(950 830).,This is approximately the difference between the temperatureof the compressed air which is leaving the regenerator and thetemperature of the exhaust air which is leaving the expander and isentering the regenerator. For the assumed r the assumed E and theassumed Ep, the exhaust air leaves the expander at a temperature ofabout 1,160R, so the compressed air is heated recuperatively to about1,040R (1 160 120) and the cycle operates at a thercause the airexpander inlet temperature (T the system pressure losses which fix Ep;the component efficiencies (E E E E the heat exchanger temperatureapproaches (AT AT the condensing temperature (T and the ambienttemperature (T are all constants for any selected system, theregenerator temperature approach (AT is a function only of T and r SinceT and r are related by the previously given (Eq. 1 for optimum r formaximum Brayton cycle work output, r is'a function only of AT Therefore,when for economic or other reasons a specific regener- T should be atleast about 1 below the ambient air 30 ator temperature approach ischosen, this choice also temperature that is ordinarily encountered. Ithas further been discovered that satisfactory results can be achievedover a range of from 10 percent greater to 10 I "EYE TH (Eq. 2), r

[ETEPTT 4ETE determines the optimum r which is required for maximum workoutput. 7

This optimum r is given by the equation.

percentsmaller than the r actually calculated.

For any chosen T there is a unique value of r at which the work producedin a Brayton cycle is a maximum. The net work output, i.e. the Braytoncycle work less the refrigeration work, depends, of course, on theefficiency of the refrigeration system which is chosen, but once therefrigeration system is chosen, at the chosen T, the net work output isa maximum at the same unique value of r at which (for the same T theBrayton cycle work output is a maximum.

It was shown previously that when the Treadwell System is used at theassumed conditions, the exhaust air must enter the heat recovery systemat 950R in order for the heat recovery system to provide therefrigeration work .which is needed when the refrigeration system coolsfrom 560R to 400R the air which is about to enter the air compressor. Itwasalso shown previously that for maximum Brayton cycle work output theoptimum r (E E E T /T 1.

As an example, assume that E 0.85; E 0.87; E, (1.05)" 1.014; T 1,960R(1,500F); and T 400R,

(0.85 X 0.87 X 1.014 X l960)/(400) 1.915 =r With this r E and T the aircompressor discharge wherein E Ep, T T and E are as previously defined;AT is the chosen regenerator temperature approach; C is the coefficientof performance of the .chosen refrigeration system at the T; at which itoperates; and C is the coefficient of performance of the chosen heatrecovery system at the T at which it operates. lt is to be noted thatalthough T does not appear explicitly in the equation, it is inherent inthe calculaculated for this T and the coefficient of performancetemperature (T is about 830R. The regenerator 6 entering theregeneratorand the temperature of the ex- C); of the chosenrefrigeration system is calculated for the same trial T The values for TE AT C C T and E are substituted in Equation 2, and the resulting r iscompared with the trial r Eq. 1. If this resulting 'r is not the same asthe trial r a new trial r is calculated from a new trial T a new C and anew C are calculated, and a new resulting r is calculated. Thisprocedure is repeated until the calculated resulting r is the same asthe calculated trial r With a regenerator temperature approach of F(requiring an extremely large and very expensive regenerator), bycalculation the suction temperature is 442R, the optimum r is 1.825, thecycle thermal efficiency is 42.8 percent, and the power production is7.7 BTU of work for each cu. ft. of air displaced by the compressor,i.e. for each cu. ft. of compressor volumetric capacity. Other thingsbeing equal, the cost of a compressor is related to its volumetriccapacity, and the cost of the compressor is a substantial part of thecost of a Brayton cycle engine. The work produced per unit of compressorcapacity is therefore, a measure of the cost of the equipment used toproduce power in a Brayton cycle engine.

With a regenerator temperature approach of 100F., the suctiontemperature is 407R, the optimum r is 1.898, the cycle thermalefficiency is 40.7 percent, and the power production is'8.6 BTU of workper cu. ft. of compressor capacity.

With a recuperator temperature approach of 120F., the suctiontemperature is 400F., th optimum r is 1.915, the cycle thermalefficiency is 40.2 percent, and the power production is 8.96 BTU of workper cu. ft. of compressor capacity. 7

With a regenerator temperature approach of 150F.,

the suction temperature is 390R, the optimum r is 1.94, the cyclethermal efficiency is 39.7 percent, and the power production is 9.42 BTUof work per cu. ft. of compressor capacity.

When no regenerator is used, and the heat of the air which is leavingthe air expander is used only to power the refrigeration system, thesuction temperature is 343R, the optimum r is 2.07, the cycle thermalefficiency i537 percent, and the power production is 12.3 BTU of workper cu. ft. of compressor capacity.

When taking suction at 560R, with an r of 1.62 and a regeneratortemperature approachof 150, in the prior art a recuperated uncooledBrayton cycle engine produces 3.94 BTU of work per cu. ft. of compressorcapacity, at a thermal efficiency of about 29.2 percent. The regeneratorof this engine exhausts at about 1,120R, and when this exhaust heat isused to make 50 psig steam in a waste heat boiler, the steam produces inan expensive separate steam turbine about 1.38 BTU of additional work,for a total of 5.32 BTU for each cu.

ft. of capacity of the air compressor of the Brayton cycle engine. Thecombined cycle thermal efficiency is about 39 percent.

With the same regenerator temperature approach of 150, an enginedesigned in accordance with the present invention has a suctiontemperature of 390R, operates with a cycle thermal efficiency of about39.7 percent, and produces a net work output of about 9.42 BTU per cu.ft. of compressor capacity, which is about 2.39'times that of theuncooled standard recuperated cycle engine and about 1.77 times that ofthe uncooled combined recuperated cycle engine. It is to be noted thatthis 9.42 BTU work output is produced by the Brayton cycle engine alone,and that there is no need for an expensive separate power producingsteam turblue.-

All of the preceding Brayton cycle examples have been based on using theTreadwell System, but with a Brayton cycle it is possible to use other,less efficient combinations of self-driven refrigeration-heat-recoverysystems. For example, a single or a multistage refrigeration system canbe powered by a heat recovery system employing a single or a multistageboiler. For a chosen 20 heat recovery system and for a chosenrefrigeration system it is necessary to give due consideration to allthe pertinent factors, such as the heat exchanger temperatureapproaches, the component efficiencies, the number of stages, and thelike, and to calculate for each specific T its coefficient ofperformance C and for each specific T its coefficient of performance CThe previously described procedure using a trial T is then employed todetermine the optimum r for a chosen nac- The preceding Eq. 2 for r is,therefore, applicable regardless of the type of refrigeration system orof the type of heat recovery system which is used.

The thermal efficiency of a prior art Brayton cycle engine suffersconsiderably if it becomes necessary to operate the engine at a reducedcapacity. For example, the previously described prior art engine, with aregenerator temperature approach of 150, an r of 1.62, and a suctiontemperature of 560R (ambient temperature 560R), operates at a designpoint thermal efficiency of 29.2 percent. When called on to operate at42 percent of its design point capacity, the same engine operates at athermal efficiency of 17.8 percent, which is only 61 percent of itsdesign point efficiency. This is because the most practical way toreduce the capacity of a prior art engine is to lower its firingtemperature, which simultaneously lowers its Carnot cycle efficiency aswell. In this example, at the design point the firing temperature is1,500F., but at 42 percent capacity the firing temperature is only1,090F.

An engine built in accordance with the present invention, with aregenerator temperature approach of 150, an r of 1.94, and a suctiontemperature of 390R (ambient temperature 560R), operates at a designpoint thermal efficiency of 39.7 percent. When this engine is called onto operate at 42 percent of its design point capacity, it operates at athermal efficiency of 29.5 percent, which is almost percent of itsdesign point efficiency. In this case, the capacity is reduced byallowing the level of suction refrigeration to rise to 560R. The enginecapacity is easily varied between 42 percent and percent of its designcapacity by adjusting the temperature level to which the suction air iscooled. (This adjustment can readily be made in various ways, forexample, by throttling the flow of cooling water to the refrigerationcondenser.) When the temperature of the suction air is raised, theengine capacity is reduced. The firing temperature remains at 1,500F.for this entire range'of engine capacities. If the firing temperature islowered, the engine capacity can be reduced to even less than 42 percentof design capacity, at the penalty of a somewhat lowered thermalefficiency.

FIG. 2 illustrates the removal of contaminants from dirty fuel,producing clean fuel for the Brayton cycle engine. Some coals havecontaminants of sulfur and particulates, and some oils have sulfur and afew also have small amounts of vanadium and nickel. The drawing isdiagrammatic as the particular design of equipment used is not changedby the'present invention.

Dirty fuel,-either solid or liquid, is partially oxidized in a reactor36. This reactor receives compressed air at about 100 psig, heated to800F., through the pipe 37. The amount of air is restricted so thatpartial oxidation takes place. SomelOO psig steam is also introducedthrough the pipe 43 to aid in the gasification or partial oxidation ofthe fuel. A product gas at about 2,350F. enters the waste heat boiler 38after having been mixed with a much larger stream, 10 mols to l, ofcooler product gas from the pipe 47. This results in lowering thetemperature of the mixture to about 850F., as indicated, a temperaturewhich is sufficiently low so that hydrogen sulfide does not corrode theboiler surfaces.

Some steam is bled out of the turbine at the low pressure stage and isrecycled through the pipe 43 to the reactor, as has been described. Theprocess gases leave boiler 38 at about 700F., pass through the pipe 47,are blown by the blower 39 through a dust collector 41 and then aresplit, about 1 mol going to a boiler feedwater heater 45,- whichsupplies the boiler with feedwater through the pipe 46, and the largerportion about 10 -mols, passing on through the pipe 47 to quench thehigh temperature product gases entering the boiler, as has beendescribed. While the volume recirculated is very large compared to thevolume produced by partial oxidation, this recirculation or recyclingconstitutes a circulating load, and about 1 mol of product gases finallyare cooled in the feedwater heater 45. There is no loss in heat as thesensible heat of the large volume of recirculated quenched gases givesup this sensible heat in the boiler 38 without significant loss.

The exhaust from the steam turbine 42 is condensed in the condenser 49and pumped by the pump 50 through the feedwater heater 45 back to theboiler 38. Makeup water to compensate for the steam used in the partialoxidation is introduced into the suction of pump 50 in the conventionalmanner. This additional water, which though needed is not a feature ofthe present invention, is, therefore, not specifically shown on thedrawing.

In the feedwater heater '45 the 750 product gas is cooled to about 150F.As in many places on the drawing, thisis an approximate temperature andis symbol- I ized by the :t symbol. The 15091 product gases are scrubbedin particulate scrubber 51, where solid mate-' of course the plant 52maybe omitted. The purified gas passes through the pipe 53 torecuperator 54, which is heated by exhaust gases from the Braytoncycle'expander 50. The gas is heated up to about 800F. and the expanderexhaust is cooled down to about 250F., passing out through the exhaustpipe 60.

In parallel with the recuperator 54 is a recuperator S9, which is alsofed with a portion of the hot exhaust gases from the expander 57.Through this recuperator, air compressed in the air compressor 22 entersthrough pipe 48 and is heated up to about 800F. The expander 56, as isnormal, produces power in excess of that required by the compressor 57and this additional power is obtained as useful work, symbolized by thegenerator 58. The hot compressed air stream is split, part of it goingto the partial oxidation reactor 36 through the pipe 37, as has beendescribed, and part of it into the Brayton cycle combustor 55, where itburns with the fuel .gases preheated by the recuperator 54.

It will be seen that the major portion of the energy in the exhaustgases from the expander 56 is effectively used in preheating air andfuel for the Brayton cycle combustor and partial oxidation reactor. Theonly significant energy losses are in the exhaust pipe 60, whichexhausts at a very much lower temperature than from an ordinary Braytoncycle expander, and a small amount lost in the particulate scrubber 51.Steam at a useful pressure and temperature is produced economically bythe waste heat boiler 38 from the large volume of quenched processgases, and the boiler operates reliably since the inlet process gastemperature is brought down to a low enough figure to prevent damage tothe heating surfaces of the boiler. This quenching, as has beendescribed, does not result in any loss of heat because the sensible heatof the large volume of gases going through the boiler is practically alleffectively utilized in raising steam.

FIG. 2 illustrates the combination of recycling a large amount of cooledpartially oxidized gases in order'to bring down the temperature in theboiler 41. With certain contaminants the relatively coolsurfaces in thewaste heat boiler 41 can tolerate a higher temperature, and where thisis possible, part or all of the recycling of the cooled gases may beomitted.

FIG. 2 illustrates the combination of cleaning dirty fuel with an openBrayton cycle system. It is particularly useful with such a system whenrefrigerated suction of the present invention is used. However, the samepartial oxidation and cleaning of the dirty fuel may be used with aclosed Braytonv cycle.

I claim:

1. An open Brayton cycle comprising, in combination, air compression,combustion, and turbo expansion of the combustion gases, refrigeratingthe air at the inlet of compression, the refrigeration includingrefrigerant evaporation and refrigerant condensation in heat exchangerelation with ambient air, and controlling refrigeration tomaintainconstant a temperature differential between the refrigerant atevaporation and condensation.

2. A cycle according to claim 1 in which the refrigeration of the airbeing compressed is to a temperature at which water vapor condenses,vaporizing the water at a pressure at least as high as the pressure ofthe compressed air, and introducing the vaporized water into the Braytoncycle between air compression and turbo expansion.

3. A cycle according to claim 2 in which the water condensation is inthe presence of an aqueous solution of a freezing point depressant.

4. A cycle according to claim 2 in which the water is condensed in thepresence of a water vapor pressure depressant.

5. A cycle according to claim 1 in which the control of therefrigeration system is by variable throttling in the suction of therefrigerant compression.

6. A cycle according to claim 5 in which the refrigeration of the airbeing compressed is to a temperature at which water vapor condenses,vaporizing thewater at a pressure at least as high as the pressure ofthe compressed air, and introducing the vaporized water intowhich'apparatus includes in the Brayton cycle an air compressor, acombustion device into which compressed air passes, means forintroducing fuel into said combustion device to burn with the compressedair, a turbo expander, and means for connecting the combus- 24 tiondevice to the inlet of the turbo expander, a refrigerating means forrefrigerating air entering the air compressor, which refrigerating meansincludes a refrigerant evaporator in heat exchanging relation with thecompressor air inlet, a refrigerant compressor and a refrigerantcondenser in heat exchange relation with ambient air, and means forcontrolling the refrigeration to produce a substantially predetermined Vconstant evaporator-condensor temperature differential.

10. An apparatus according to claim 9 in which the control ofrefrigeration is by throttling means on the suction of the refrigerantcompressor.

1. An open Brayton cycle comprising, in combination, air compression,combustion, and turbo expansion of the combustion gases, refrigeratingthe air at the inlet of compression, the refrigeration includingrefrigerant evaporation and refrigerant condensation in heat exchangerelation with ambient air, and controlling refrigeration to maintainconstant a temperature differential between the refrigerant atevaporation and condensation.
 2. A cycle according to claim 1 in whichthe refrigeration of the air being compressed is to a temperature atwhich water vapor condenses, vaporizing the water at a pressure at leastas high as the pressure of the compressed air, and introducing thevaporized water into the Brayton cycle between air compression and turboexpansion.
 3. A cycle according to claim 2 in which the watercondensation is in the presence of an aqueous solution of a freezingpoint depressant.
 4. A cycle according to claim 2 in which the water iscondensed in the presence of a water vapor pressure depressant.
 5. Acycle according to claim 1 in which the control of the refrigerationsystem is by variable throttling in the suction of the refrigerantcompression.
 6. A cycle according to claim 5 in which the refrigerationof the air being compressed is to a temperature at which water vaporcondenses, vaporizing the water at a pressure at least as high as thepressure of the compressed air, and introducing the vaporized water intothe Brayton cycle between air compression and turbo expansion.
 7. Acycle according to claim 6 in which the water condensation is in thepresence of an aqueous solution of a freezing point depressant.
 8. Acycle according to claim 6 in which the water is condensed in thepresence of a water vapor pressure depressant.
 9. An apparatus forcarrying out a Brayton cycle, which apparatus includes in the Braytoncycle an air compressor, a combustion device into which compressed airpasses, means for introducing fuel into said combustion device to burnwith the compressed air, a turbo expander, and meaNs for connecting thecombustion device to the inlet of the turbo expander, a refrigeratingmeans for refrigerating air entering the air compressor, whichrefrigerating means includes a refrigerant evaporator in heat exchangingrelation with the compressor air inlet, a refrigerant compressor and arefrigerant condenser in heat exchange relation with ambient air, andmeans for controlling the refrigeration to produce a substantiallypredetermined constant evaporator-condensor temperature differential.10. An apparatus according to claim 9 in which the control ofrefrigeration is by throttling means on the suction of the refrigerantcompressor.